Gaseous oxygen monitoring systems are useful for monitoring combustion, waste gases, atmospheric oxygen concentration, and chemical processes, as examples. To meet these requirements, a variety of methods for gaseous oxygen detection have been explored and developed. Significant attention has been given to the development of optical fiber based chemical sensors (OFCSs) for oxygen sensing [See, e.g., C. H. Jeong et al., “Application of the channel optical waveguide prepared by ion exchange method to the preparation and characterization of an optical oxygen gas sensor”, Sens. Actuators B 105 (2005), pp. 214-218; B. J. Basu et al., “Optical oxygen sensor coating based on the fluorescence quenching of a new pyrene derivative”, Sens. Actuators B 104 (2005), pp. 15-22; Y. Fujiwara, et al., “Novel optical oxygen sensing material: 1-pyrenedecanoic acid and perfluorodecanoic acid chemisorbed onto anodic oxidized aluminum plate”, Sens. Actuators B 99 (2004), pp. 130-133; D. L. Plata et al. in “Aerogel-platform optical sensors for oxygen gas”, J. Non-Cryst. Solids 350 (2004), pp. 326-335; Y. Fujiwara, et al., “Optimising oxygen-sensitivity of optical sensor using pyrene carboxylic acid by myristic acid co-chemisorption onto anodic oxidized aluminium plate”, Talanta 62 (2004), pp. 655-660; P. A. S. Jorge et al., “Optical temperature measurement configuration for fluorescence based oxygen sensors”, Proceedings of SPIE—The International Society for Optical Engineering; vol. 5502 (2004), pp. 279-282; N. Leventis et al., “Synthesis and Characterization of Ru (II) Tris (1,10-phenanthroline)—Electron Acceptor Dyads Incorporating the 4-Benzoyl-N-methylpyridinium Cation or N-Benzyl-N-methyl Viologen. Improving the Dynamic Range, Sensitivity, and Response Time of Sol-Gel-Based Optical Oxygen Sensors”, Chem. Mater. 2004, 16, pp. 1493-1506; O. S. Wolfbeis, “Fiber-optic chemical sensors and biosensors” Anal. Chem. 2004, 76, pp. 3269-3284; Y. Amao, “Probes and polymers for optical sensing of oxygen” Microchim. Acta 143 (2003), pp. 1-12; D. Jiang et al., “Optical fiber oxygen sensor based on fluorescence quenching”, Acta Optica Sinica 23 (2003), pp. 381-384; K. Eaton et al., “Effect of humidity on the response characteristics of luminescent PtOEP thin film optical oxygen sensors”, Sens. Actuators B, 82 (2002), pp. 94-104; K. Mitsubayashi et al., “Bio-optical gas-sensor (sniffer device) with a fiber optic oxygen sensor” in: Conference on Optoelectronic and Microelectron Materials and Devices, Sydney, NSW, Australia Dec. 11-13, 2002, p. 213-16; M. Kölling et al., “A simple plastic fiber based optode array for the in-situ measurement of ground air oxygen concentrations” in: Proceedings of SPIE—The International Society for Optical Engineering; vol. 4576 (2002), pp. 75-86; A. A. Kazemi et al., “Fiber optic oxygen sensor detection system for aerospace applications” in: Proceedings of the SPIE—The International Society for Optical Engineering; vol. 4204 (2001), pp. 131-138; G. Vishnoi et al., “A new plastic optical fiber sensor for oxygen based on fluorescence enhancement” Opt. Rev. 5, No. 1 (1998), pp. 13-15; A. Mills, “Controlling the sensitivity of optical oxygen sensors”, Sens. Actuators B 51 (1998), pp. 60-68; and L. Xin et al., “Luminescence quenching in polymer/filler nanocomposite films used in oxygen sensors” Chem. Mater. 13 (2001), pp. 3449-3463.]. Optical fiber based chemical sensors have small size and flexibility which render these sensors useful for in situ and in vivo sensing. Since the optical fibers used for OFCSs can transmit chemically-encoded information between a remote sample and a spectrometer, the optical fiber based sensors are suitable for in situ monitoring of environmental hazards in hostile or not readily accessible environments. In addition, optical fibers are relatively insensitive to noise from radioactivity and electric fields, and signals acquired with optical fibers are less affected by environmental interferences than those transmitted through electrical wires. Optical fibers can also transmit a high density of information. Wavelength, polarization, and phase information enhances both the quality and quantity of chemical information obtained by OFCSs.
For the past few years, optical sensors for oxygen sensing have been based on dynamic quenching of luminescence generated in chemical or photo reactions. The principle of photo-luminescent or photoexcited state quenching of organic dyes by oxygen is described in Y. Amao, supra; A. Mills, supra; and R. Ramamoorthy et al., “Oxygen sensors: materials, methods, designs and applications” J. Mater. Sci. 38 (2003), pp. 4271-4282, as examples. Typically, this type of optical oxygen sensor is composed of organic dyes, such as polycyclic aromatic hydrocarbons (pyrene, pyrene derivatives, etc.), transition metal complexes (Ru2+, Os2+, Ir3+, etc.), metalloporphyrins (Pt2+, Pd2+, Zn2+ etc.) and fullerene (C60 and C70), immobilized in oxygen-permeable polymer films [See, e.g., Y. Amao, supra.]. The quenching of the luminescence may be characterized by the Stern-Volmer equation, and several oxygen sensors having various sensitivities have been developed using this principle [See, e.g., A. Mills, supra.]. However, the Stern-Volmer quenching constant is sensitive to the oxygen diffusion coefficient for the encapsulating medium [See, e.g., A. Mills, supra.]; therefore, it is difficult to control the repeatability and uniformity of such sensors.
Accordingly, it is an object of the present invention to provide an apparatus and method for detecting oxygen having good repeatability and response time.
Additional objects, advantages and novel features of the invention will be set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.